Means for and method of modulation



Nov. 13, 1923.

L. ESPENSCHIED MEANS FOR AND METHOD OF NODULATIGN Filed Dec. 16. 1920 IN V EN TOR- V lave/walled ATTORNEY Patented Nov. .13, 1923;

v I 1,413;514. UNITED {STATES PATENT OFFICE.

LLOYD ESPENSCHIED,. OF QUEENS, NEW YORK, ASSIGNOR TO AMERICAN TELEPHONE .AND.'1ELIEGIRAIPHCOMPANY, A CORPORATION OF NEW YORK.

'u mnsronnnn HE'I'HODOF monnnarron.

Application filed December 16,1920. Serial No. 481,191.

To all whom it concem:

Be it known that I, LLOYD ESPENSCHIED, residing at Queens, in the county of Queens and State of New York, have invented oer-- tain Improvements inv Means for and Methods of Modulation, of. which the following is a specification.

This invention relates; to transmission by means of carrier currents for either radio or wire purposes, and more particularly to means for and methods of modulating carrier currents in accordance with signals,

It has heretofore been proposed to modulate alternating carrier current in accordance with signals by means of a magnetic modulator, a well-known type of which is described in the U. S. patent to Alexanderson No. 1,206,643, November28, 1916. In accordance with the present invention, however, it is proposed to take advantage of a peculiar property of the temperature-penneabihty characteristic of an iron core. As is well' known, at a certain critical point in the temperature-permeability characteristic of an iron core known as t the permeability of the core undergoes a rapid change. By working the core of a. magnetic modulator at or near the recalescent point, a greater modulating effect may be obtained in accordance with the present invention because-of the rapid change in permeability at this point.

The invention may now be more fully understood from a detailed. description thereof when read in connection with the accompanyingdrawing, Fi res 1 and 2- of which are curves illustrating the properties of an iron core coil, Figs. 3 and 4 of which arecircuit diagrams showing appa-ratusfor operating in accordance with one method embodying the invention, Figs, 5 and 6 of which are schematic arrangements showing structures for heating the iron core of the magnetic modulator and Fig. 7 of which is a ircuit diagram-showing apparatus for operating in accordance with another'method embodying the invention.

Referring to Fig. 1, the curve indicates roughly the temperature-permeability characteristic of. an iron core up to the critical temperature known as the recalescent point. It will be seen from an examination of this curve that the permeability is a very rapid recalescence.

e recalescent point,

permeabilit and at .t

centigrade. For temperatures in this re 'on the B-H curve also undergoes a mar ed change, as is indicated in Fi 2, in which the curve 1 represents the B- curve under normal conditions, while 2 indicates the B-H curve at or about the .condition of It. will beobserved from the curve 2 that, for small magnetizing forces, the magnetic induction B, and hence the permeability, rises much more. rapidly for temperatures near the critical frequency than in the case of the curve 1, which indicates the characteristic for normal temperatures.

In taking advantage of the phenomena of recalescence for magnetic modulation, it is possible to utilize either the characteristic indicated by the curve of Fig. 1 or the characteristics indicated by the curve 2 of Fig.

2. A circuit arran ement for employing the characteristic of Fig. 1 is illustrated in Fig. 3. In this figure A is a transmitting antenna coupled through a transformer T to a tuned circuit includlnga source of carrier oscillationsa tuning condenser C and a magnetic modulator MM, comprising an iron core 11 and a winding 10. The winding 10 is serially included in circuit with the generator G while the core is included in a circuit, including a battery or other source of heating current B, a resistance R for regulating the amount of heating currentpassing throu 'h the iron core 11 and a microphone M For impressing voice currents upon the modulator; In operation, the resistance R is adjusted so that the current-passing through the iron core 11 will heat it to the recalescent point. As will be seen from the curve of Fig. 1, when thecore is heated to this point a slight change in temperature produces a .ver considerable change in the o the coil of the modulator. Consequent y, when themicrophone M is operated,-the variations in the current flow through the circuit including the battery B producevariations in the temperature of the core 11 and the con permeability in the (x111 of the modulator uent' changes in the.

MM result in large changes in the amplitude of the oscillations supplied by the generator G through the transformer T to the an-- tenna A.

In order that the iron core of the coil MM may be heated by an electric current e same time be capable of producing a considerable magnetic flux in the coil,

it-may be constructed in the form of a file ment orfilaments 11', looped back and forth through the coil 10, as illustrated in Fig. 5. These filaments are included serially in the circuit of the battery B, resistance R and microphone M, so that the current flowing through the filaments raises the temperature thereof. In order to prevent rapid oxida tion, the filaments forming the core of the inductance coil may be mounted in a. container 12 of glass or other suitable material, the said container being evacnatedin a well-known manner and provided with terminals for the purpose of connecting the filamentary core to the microphone circuit and for connecting the windings of the inductance coil to the generator circuit.

Another manner in which the core may be constructed is illustrated in Fig. 6. In this case, the core 11 is made up of a number of flat plates or laminations, as is well understood in the art and between each pair of laminations or between certain of the laminations a heating element 13 of the resistance type may be placed. The terminals of the heating element or elements may then be connected to the circuit, including the battery B, microphone M and resistance B, so that the laminations of the core will be heated by contact with the heating element 13. In this case, variations in the current flowing through the heating element will produce changes in the temperature of the core and, consequently, changes in the permeability of the coil, so that the carrier frequency supplied by the alternator will be modulated in accordance with the signal variations.

Another circuit arrangement for employing a modulator of the type illustrated in Figs. 5 and 6 is shown in Fig. 4. In this case, the modulator MM is not included in the series circuit including the primary of the transformer T, the generator G and the condenser C, but is inserted serially in the ground connection of the antenna A. The

si naling circuit, including the microphone is associated with "the modulator MM, however, in the same manner as in Fig. 3. The operation will be obvious from the operation already described in connection with Fig. 3 and, consequently, need not be referred to here.

As already stated, instead of modulating by changing the temperature, the modulation may be controlled in accordance with the signal by varying the magnetic force under conditions such that the core of the coil is heated to the recalescence point. As shown by the curve 2 of Fig. 2 for small applied magnetic forces, the magnetic induction B changes rapidly and if the magneticforce varies in accordance with the signal, large variations in the rmeability of the coil will result. Fig. illustrates a circuit arrangement for utilizing this characteristic. In this circuit diagram 14 designates the core of a magnetic modulator of the general type disclosed in the patent to Alexanderson, above referred to. Coils 15 and 16 are connected in parallel in a circuit including the condenser C, said circuit being connected to the generator G in shunt with the antenna A. The coils 15 and 16 are wound upon the core 14 in such a manner as to normally aid each other around the two inner limbs. Another coil 17 is included in circuit with a battery B,, a microphone M and a resistance ,R, and is wound to affect alike the two inner limbs of the core 14: in such a manner as to produce changes in the permeability thereof, with changes in the applied magnetic force, these changes being produced by changes in the.

direct current flowing through the coil, in response to the actuation of the microphone Me It is, of course, obvious that a vacuum tube amplifier may be included in this circuit for the purpose of increasing the signalin energy. Additional coils 1S and 19 are a so wound upon the core, these coils being included in circuit with the battery B and resistance R Reaction between the high frequency windings 15, 16 and the heating circuit of windings 18, 19 is prevented by the reactance of choke coil 20. The resistance R, is adjusted so that the current flowing through these coils will heat the core up to the recalescence point. With the core thus heated, relatively small changes in the current flowing through the coil 17 will produce large changes in the permeability of the core and in accordance therewith, large changes in the inductance included in series with the condenser C will result, so that more or less current from the generator G is shunted from the antenna A. depending upon the instantaneous magnitude of the signaling current. The signaling current obviously may be telegraphic instead of telephonic in which case the micro plione M is replaced by a telegraph key or re a lt will be obvious that the general principles herein disclosed may be embodied in many other organizations widely different from those illustrated, without departing from the spirit of the invention, as defined in the following claims.

What is claimed is:

1. In a modulating'system comprising a carrier source and an inductance, the method of modulating a carrier frequency in accordance with signals which consists in subjecting the energy of the carrier source to the action 'of said inductance, maintaining the temperature of said inductance in the neighborhood of the recalescence point, and varying the permeability of said inductance in accordance with a signal.

- 2. In a modulating s stem comprising a carrier source and an in uctance, the method of modulating a carrier frequency in accordance with signals which consists in assing the energy from the carrier source t rough .said inductance, maintaining the temperature of said inductance near the recalescence point, and varying the permeability of sald inductance in accordance with a signal.

3. In a modulating .s stem comprising acarrier source and an in uctance, the method of modulating a carrier frequency in accordance with signals which consists in subjecting the energy of the carrier source to the action of saidinductance, maintaining the temperature of the core of said inductance in the neighborhood of the recalescence point, and varying the permeability of said inductance in accordance with a signal.

4. -In a modulating s stem comprising a carrier source and an in uctance, the method of modulating a carrier frequency in accordance with the signals which consists in subwhich consists in subjecting the energy of the carrier source to the action of said inductance, translating the energy of said electric circuit to heat, heating the core of said inductance by means of said heat to maintain its temperature in the neighborhood of the recalescence point, and varying the permeability of-said inductance in accordance with a signal.

6. In a modulating apparatus a source of carrier current, an inductance for controlling the energy .of said source,means to maintain the temperature of said inductance in the neighborhood of the recalescence oint and means to vary the permeability 0 said inductance in accordancewith a signal.

7 In a modulating apparatus a source of carrier current, an inductance for controlling the energy of said'source, means to maintain the temperature of the core of said inductance in the neighborhood of the recalescepce point, and means to vary the permeability oisaid inductance in accordance with a signal.

8. In a modulating apparatus a source of carrier current, an inductance for controlling the energy of said source, a circuit for supplying current to heat said inductance to a temperature in the neighborhood of the recalescence point, and means for varying the permeability of said inductance in accordance with a signal.

9. In a modulating apparatus a source of l carrier, current, an inductance for controlsupplying current to heat the core of said inductance to .a temperature in the neighborhood of the recalescence for varying the permeability of said inductance in accordance with signals.

10. In a modulating apparatus a source of oint, and means carrier current, an inductance for controlling the energy of said source, means for heating said inductance to a temperature in the neighborhood of the recalescence point,

and means to vary the magnetic force applied to said inductance in'accordance with signals, whereby corresponding variations in the permeability-of said inductance are produced.

In testimony whereof, I have signed m 'name to this specificationthis 13th day of December 192 LLOYD ESPENSCHIED.

70 ling-the energy of said source, a circuit for 

